1. Field of the Invention
The present invention relates to a transmitting device that transmits the same information such as broadcast information to a plurality of receiving devices by use of a multicarrier transmission system and to the receiving device.
2. Description of the Related Art
Research and development have been progressed for a long time about a technology of transmitting the same broadcast information comprised of image data, voice data, etc as in the case of a TV broadcast, a radio broadcast, etc to a plurality of receiving stations. As to this type of technology, Patent document 1 discloses a technology of efficiently transmitting the broadcast information.
This related art is that a transmitting station generates plural data having different levels-of-detail (levels of data compression) about the same information, and transmits the respective pieces of data via a plurality of transmission channels, separately. FIG. 20 is a diagram showing an example of a transmitting method in this related art, and FIG. 21 is a diagram illustrating an example of information allocation related to the transmitting method in the related art.
In the examples illustrated in FIGS. 20 and 21, the plural data (#1 through #3), (#1 through #6) and (#1 through #9) having the different levels-of-detail, which comprises the same broadcast information, are generated. To be specific, the respective pieces of data are generated in a way that increases the level-of-detail of the broadcast information in the sequence of (#1 through #3), (#1 through #6) and (#1 through #9) and also increases a data size. Transmission of the data involves employing transmission channels CH1,CH2 and CH3 corresponding to receivable bandwidths of a receiving station, wherein each transmission channel is set to raise a transmission rate in the sequence of CH1, CH2 and CH3. The base station allocates the data to the channels having the lower transmission rate in the sequence from the smallest level-of-detail, and simultaneously transmits the broadcast information.
On the other hand, each receiving station sets the receivable band to any one of the transmission channels CH1, CH2 and CH3 corresponding to the receiving environment of the self-station, and receives the broadcast information that is transmitted from the base station. For example, the receiving station, which is in the good receiving environment, receives the broadcast information via the transmission channel CH3 having the high transmission rate and can therefore receive the broadcast information having the high level-of-detail. Conversely, even the receiving station, which is in the poor receiving environment, can receive the broadcast information via the transmission channel CH1 having the low transmission rate and can therefore receive the broadcast information, though low of the level-of-detail.
Namely, according to the related art, each receiver can receive the same information such as the broadcast information at the transmission rate (the level-of-detail) corresponding to the receiving environment.
The Patent document 1 is a “Japanese Patent Application Laid-Open Publication No. 2004-32604”.
In the related art described above, however, N-staged adjustment of the transmission rate entails using N-pieces of transmission channels, and it is required that the same items of information having different levels-of-detail be allocated to the respective channels. In this case, the information (#1 through #3 in FIG. 21) having the minimum level-of-detail is allocated to all of the N-pieces of transmission channels.
Accordingly, if the related art described above takes a scheme enabling the transmission rate to be adjusted in detail at multi-stages, it follows that the information of the low level-of-detail is transmitted via the same number of channels as the number of rate-adjustable stages, resulting in a problem that the frequency usage efficiency declines.
Thus, the related art is, in the communication system of transmitting the same information such as the broadcast information to the plurality of receiving stations, hard to enable the transmission rate to be adjusted at the multi-stages and is disabled to sufficiently improve the transmission efficiency.